This invention relates to a cardiac pacemaker including means for controlling the stimulation frequency conformed to the bodily stressing conditions of the wearer of the pacemaker. The electro-stimulation of the heart today is that therapy of selection of a number of bradycardic disturbances of the cardiac rhythm, which can hardly or at least not on the long run be influenced by medicamentous treatment and the prognosis of which were very serious prior to the employment of pacemakers. The primary goal of pacemaker employment initially was to prevent the cardiac standstill (asystole) which caused loss of conciousness occurring in attacks, often with the consequences of a stroke or even with a fatal end. This goal has today broadly been achieved, and the pacemaker method is practiced with great success for patients having such syndromes, everywhere.
A second indication for the cardiac pacemaker therapy to an increasing degree is the bradycardiac insufficiency, i.e. the development of heart weakness by virtue of an insufficient frequency regulation. For while the sound heart by increasing the heart frequency is able to increase its performance according to the bodily requirements, heart-sick patients with bradycardic heart rhythm disturbances in many instances are not able to do so any more. The form of cardiac pacemaker stimulation performed up to now also brings about no decisive improvement in this aspect, since the frequency of stimulation (generally 70/min) is fixed and is not variable.
Therefore, there has been no lack of attempts to control the pacemaker stimulation frequency via physiological parameters such as the frequency of breathing or the pH of the venous blood, with the aim of increasing the frequency of stimulation with a corresponding alteration of these parameters. These systems give rise to a number of new problems, however:
The implantation of a pacemaker controlled by the frequency of breathing requires a thoracotomy for implanting a pressure sensor into the pleural cavity, which is an unequally more serious operation as compared with the usual operation method of transvenous electrode displacement.
For the pH controlled pacemaker, the problem of a reliable pH measurement over extended periods of time has not been completely solved up to now. Additionally, the pH cannot be considered to be an optimum parameter for controlling the frequency of the cardiac pacemaker, since this parameter is not only dependent on the heart time volume, but also on other parameters such as breathing, the buffer capacity of blood, the kidney function and the application of certain medicines.